1. Field of the Invention
This invention relates to the field of acoustical listening devices. More particularly, the instant invention relates to an improved stethoscope head having a sound enhancing conical shell-like acoustic chamber.
2. Description of the Prior Art
Medical stethoscopes are commonly used in the health care field to detect and transmit biological sounds made by the human body. These sounds are used by the medical practitioner in diagnosing a wide variety of problems including those of the heart and lungs. The act of listening to sounds arising within organs as an aid to diagnosis and treatment is called auscultation. The medical practitioner compares the sounds perceived while auscultating the patient to those considered "normal" and thereby assesses the patients physical condition. Therefore, it is important for a stethoscope to accurately transmit the sounds detected to the medical practitioner as to enable him to accurately assess the patients condition.
The human body produces sounds across a broad spectrum of frequencies. Low-frequency (20 to 80 Hz) sound waves are common to both normal and pathological heart and lung activity, while higher frequency (80 to 800 Hz) sound waves are produced by certain murmurs and abnormal lung conditions. As a result, the human body simultaneously produces sounds across this broad spectrum making if difficult for the medical practitioner to distinguish between sounds produced by particular parts of the anatomy.
A number of stethoscope designs attempt to provide increased sensitivity to sound waves existing on either the high or low end of the frequency spectrum. These efforts have resulted in the development of two types of stethoscope heads, commonly referred to as the bell type and the diaphragm type. It has been found that the bell type stethoscope head provides greater sensitivity to low frequency sounds, while the diaphragm type stethoscope head provides greater sensitivity to higher frequency sounds. Furthermore, it has been found that as a bell chamber depth increases, its performance improves. Bell chamber depth, however, has been limited by the practical need for a compact and lightweight stethoscope head.
The prior art reveals an effort to incorporate both type of heads into a common stethoscope head body. However, incorporating both devices into a single stethoscope head has proven difficult, resulting in bulky and intricate devices that often do not allow the medical practitioner to simultaneously listen to both high and low frequency sounds. Therefore, there exists a need for an improved stethoscope head capable of delivering an optimum balance of low and high frequency sounds; also there exists a need for a stethoscope head that detects sounds produced by the heart while masking unwanted background sounds.
The prior art reveals a number of such complicated designs which provide a dual stethoscope head incorporating both bell type and diaphragm type heads. Since these inventions are often limited in the sense that the bell and diaphragm components function independently and are not capable of simultaneous operation, the inventions often do not permit the medical practitioner to simultaneously hear both low and high frequency sounds.
For example, U.S. Pat. No. 3,951,230 issued to Littmann discloses a multi-chamber stethoscope wherein a diaphragm sound chamber is disposed within a housing which allows for the head to be used independently as a diaphragm sound chamber or a bell sound chamber. Incorporating both heads into a single unit of acceptable size requires compromising performance as available chamber space is limited. In addition, combining both heads in sliding engagement requires tight tolerances and an abundance of hardware greatly complicating manufacturing costs and further compromising performance.
U.S. Pat. No. 4,212,368 issued to Allen suffers from similar flaws. The Allen patent discloses a stethoscope head having a bell and a diaphragm, the bell axis intersecting the diaphragm axis at an acute angle, and a selectively movable valve provided to connect the bell and the diaphragm, individually, to the sound tube. This arrangement also does not permit the medical practitioner to simultaneously hear both high and low frequency sounds. Furthermore, this design requires an abundance of intricate hardware and movable components that increase cost and adversely affect reliability and performance.
U.S. Pat. No. 4,903,794 issued to Klippert, discloses a stethoscope head incorporating a curvilinear convex diaphragm for interfacing with the site being auscultated, and an enclosed acoustic chamber for enhancing the fidelity of the received sounds. While the Klippert invention does allow the medical practitioner to listen to a broad spectrum of sound, it requires the use of machined enclosed acoustical chambers which require extreme manufacturing tolerances and are thus costly to fabricate.
As has been described, incorporating two different auscultating devices into a single stethoscope head has proven difficult, and resulted in bulky and intricate devices that, by enhancing sounds at extreme ends of the frequency spectrum, only allow the medical practitioner to listen to sounds within a relatively narrow frequency range. Therefore, there exists a need for an improved stethoscope head capable of delivering an optimum balance of low to high frequency sounds, thus providing the medical practitioner with a complete sound profile while masking unwanted background sounds.